This invention relates to a laser diode and a fabrication method thereof, more particularly to a laser diode which radiates with a selected light wavelength.
Laser diodes are employed for light source in optical transmission systems for example. In order to decrease influence of wavelength dispersion in optical fibers, laser diodes are required to radiate with a single wavelength. For the requirement, diffraction gratings are fabricated in waveguides of the diodes. A distributed feedback in laser diode (DFB-LD) employing the grating is described in "Optical Integrated Circuit--foundation and application", April 1988, Asakura shoten, Japan, for example.
In the prior DFB-LD, thickness of a medium is periodically changed to perform the grating. Thereby refractive index of a waveguide region is periodically changed. Then a light wavelength is selected in correspondence with the period of the grating, so that the DFB-LD radiates with the selected wavelength.
However, the prior DFB-LD has a stop band with bragg wavelength corresponding to the grating. Accordingly radiation is induced with two wavelengths around the bragg wavelength.